1. Field of the Invention
The present invention relates to a coil component including: a bar-like core not including a flange part; and a winding part (coil) formed of a conducting wire that is wound in a plurality of layers around the longitudinal outer periphery of the core.
2. Description of the Related Art
For example, in some cases, an antenna coil component (a coil component for a tag) is buried in the body of an animal to be used for ID registration for individual identification. In order to enable such a coil component to be housed in a cylindrical minute capsule, downsizing thereof is required, and, particularly the size thereof in the radial direction or the width direction is required to be, for example, as small as 5 mm or less.
In view of the above, a structure not including a flange part at its end parts is applied to a core around which a conducting wire is to be wound. This is advantageous in downsizing, and also is advantageous in accuracy of the shape of the core and occurrence suppression of warpage. In the case of using such a core not including a flange part, however, when a conducting wire is wound in a plurality of layers around the longitudinal outer periphery of the core according to a solenoidal winding method, winding collapse is likely to unfavorably occur at an end part of a winding part.
According to the solenoidal winding method, a conducting wire is wound from one end to another end to form a first layer, and the conducting wire is then turned back in the opposite direction from another end to one end to continuously form a second layer on the first layer. Then, when the turned-back second layer is wound on an end part of the first layer at the turned-back portion of the end part in the winding width direction, winding collapse is likely to occur. The winding collapse causes a trouble in coil characteristics. Moreover, if winding of the conducting wire is continued without solving the winding collapse, partial thickening occurs due to the winding, and the resultant disordered winding appearance hinders downsizing. For the coil component for a tag described above, which requires particular downsizing, insertion thereof into a minute capsule is not possible unfavorably.
In order to prevent such winding collapse as described above, it is conceived to fix the conducting wire in the winding part using a fusion wire. The fusion wire is formed by applying a bonding agent such as bond to a conducting wire, and serves to prevent winding collapse by joining turns of the wound conducting wire to each other. Unfortunately, the bonding agent is melt by heat, and the winding shape is deformed, resulting in unstable characteristics. Further, the bonding agent is thermally expanded, and a stress is applied to the core, resulting in an increase in stress resistance characteristics. Accordingly, measures to prevent winding collapse without using such a fusion wire are preferable.
Further, although not intended for measures to prevent winding collapse, at the time of the transition from a lower layer to an upper layer at an end part of the winding part, winding of the upper layer is started with a shift corresponding to one turn, whereby a wedge-like space is formed between an end surface of a flange part of the core and the winding wire. Such a technique is disclosed in Japanese Laid-Open Patent Publication No. 2006-66468A.
The winding structure disclosed in Japanese Laid-Open Patent Publication No. 2006-66468A can be expected to produce a slight effect of preventing winding collapse with reference to the drawings, but a shift corresponding to one turn is unrealistic in actual winding of a thin conducting wire. in particular, such a shift is almost impossible when a conducting wire is manually wound. Further, even if such a shift corresponding to one turn is possible, the winding at an end of the lower layer loosens, and the upper-layer conducting wire enters gaps between turns of the lower-layer conducting wire in many cases, instead of being wound on top of the lower-layer conducting wire. Accordingly, this is not an effective technique.
The flange part is formed in the core disclosed in Japanese Laid-Open Patent Publication No. 2006-66468A, and winding collapse of the winding part is substantially prevented by the flange part. Hence, the formation of the flange part is essential. Accordingly, the size of the coil component is large, so that the requirements for the antenna coil component (the coil component for a tag) as described above cannot be satisfied.
The present invention, which has been made in view of the above-mentioned circumstances, has an object to provide a coil component that can achieve downsizing thereof without providing a core with a flange part and enables solenoidal winding so as not to cause winding collapse without using a fusion wire.